Three methods were used to fabricate ZnO-based room temperature liquid petroleum gas (LPG) sensors having interdigitated metal-semiconductor-metal (MSM) structures. Specifically, devices with Pd Schottky contacts were fabricated with: (1) un-doped ZnO active layers; (2) Pd-doped ZnO active layers; and (3) un-doped ZnO layers on top of Pd microstructure arrays. All ZnO films were grown on p-type Si(111) substrates by the sol-gel method. For devices incorporating a microstructure array, Pd islands were first grown on the substrate by thermal evaporation using a 100 μm mesh shadow mask. We have estimated the sensitivity of the sensors for applied voltage from –5 to 5 V in air ambient, as well as with exposure to LPG in concentrations from 500 to 3,500 ppm at room temperature (300 K). The current-voltage characteristics were studied and parameters such as leakage current, barrier height, reach-through voltage, and flat-band voltage were extracted. We include contributions due to the barrier height dependence on the electric field and tunneling through the barrier for the studied MSM devices. The Pd-enhanced devices demonstrated a maximum gas response at flat-band voltages. The study also revealed that active layers consisting of Pd microstructure embedded ZnO films resulted in devices exhibiting greater gas-response as compared to those using Pd-doped ZnO thin films or un-doped active layers.
Data networks and new mobile networks (4G and 5G) deploy packet switching in their core networks. Due to this architecture VoIP protocols has a wide deployment in these environments. VoIP capacity and quality must be considered during VoIP protocols implementations. The aim of QoS mechanisms is to satisfy voice traffic requirements; this is deployed by using many tools like congestion management utilities, congestion avoidance utilities, and link fragmentation tools. Each tool has an impact on voice performance. Queuing is very important mechanisms in the traffic management system. Certain routers in data networks must deploy some QoS tools that control how different packets are temporally buffered until transmission on the interface. This paper studies the effect of different QoS tools on VoIP application performance and capacity via OPNET simulation. Also, the maximum VoIP capacity which gives accepted quality will be investigated.
The use of thermal insulation is one of the most crucial solutions for reducing energy consumption when designing buildings. In this study, we investigate the use of various types of thermal insulation (air, cellulose, fiberglass, mineral wool, polystyrene, and polyurethane foam) to determine the best location when designing. The numerical study is done using ANSYS/FLUENT 16 software and an enthalpy-porosity formalism. According to the study's findings, all heat insulators investigated offer effective insulation, but some of them, like air, have characteristics that make them challenging to employ. The remaining insulators satisfy all requirements for usage as a thermal insulator. Given that it possesses all the necessary characteristics to be used as a thermal insulator, (polystyrene) is one of the most important insulators that are readily available locally. The use of thermal insulation in buildings reduces the need for refrigeration equipment to maintain comfortable conditions, which has a significant negative impact on the environment.
This work presents a numerical study of improving heat transfer to PCM (paraffin wax) inside a rectangular cell using copper rods. The numerical study is conducted using an enthalpy–porosity formulation in (ANSYS/FLUENT software16). The phase replacement material used in this study is paraffin wax (RT58). This study aims at improving heat transfer and absorption within phase-changing materials. The work demonstrates the effect of the presence and number of copper rods in the cell on heat transfer and the effect of this on time required to finish the melting process, thus improving the heat storage or absorption process. It is found that using copper rods inside cell filled of PCM increases the feasibility process and decreases the time to complete the melting process in the rate of 50%. It is also found that increasing the number of rods from three to five increases the melting process in the rate of 10%. In contrast, increasing number of rods decreased the time to complete the melting process.
Distributed Photovoltaic applications bring considerable benefits to the distribution network, especially in regions with high irradiation levels. This work contributes to the efforts of adapting Distributed Photovoltaic applications in Iraq, as it has high irradiation levels. The development of a Photovoltaic physical model for Distributed Photovoltaic installations under actual weather conditions has been presented. Additionally, the impact of Distributed Photovoltaic installations connected at downstream points of distribution feeders on the voltage profile along those feeders has been discussed. Based on that, a suitable procedure to assess this impact has been developed under four different scenarios. A case study of the existing 11 kV feeder in Baghdad has been used to apply the developed procedure by considering different scenarios of Distributed Photovoltaic integration. The case study concluded no over-voltage issues along the feeder, even with the extreme conditions of applied scenarios, related to voltage level at the feeder head, capacity and location of the Distributed Photovoltaic plant, and load/ Distributed Photovoltaic profiles of summer and winter.
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